Locking circuit with double signal control



July 4, 1950 E. R. sHl-:NK ET AL LOCKING CIRCUIT WITH DOUBLE sIGN'ALcoNTRoL 2 she'ts-sheet 1 Filed Deo. l, 1944 July 4, 1950 E. R. sHENKETAL LOCKING CIRCUIT WITH DOUBLE SIGNAL CONTROL 2 SheetsA-Sheet 2 FiledDec.

m m r Y M. n I H @www J 7 ,w m ww ms Patented July 4, 1950 LOCKINGCIRCUIT WITH DOUBLE SIGNAL CONTROL Eugene R. Shenk and James R. Weiner,Brooklyn, N. Y., assignors to Radio Corporation of America, acorporation of Delaware Application December 1, 1944, Serial No. 566,129

(Cl. Z50- 27) 6 Claims.

This application. relates to electronic polar relays. Relays of thistype have wide application in the radio art. A, particular applicationis use. of, the same in two-tone telegraph systems. These systems areknown also as frequency shift telegraphy systems. n

An object of this invention is improved' relaying of currentsA orpotentials.

A more speci'c object of this invention is to provide an electronicequivalent of mechanical' polar relay that is capable of' much greateroperating. speeds.

In its, broadest aspect this. invention comprises a locking `circuitsomewhat of the. type disclosed.

in. Finch U; S. Patent #1,844,950, dated February 16, 1932. Means: isprovided. to subject the control grid of one tube of the. locking.circuit to a. net bias controlled by two independent voltages. Suitablechanges are required in these` independent voltages to cause an actionin the locking circuit. p

In. accordance with this invention the independent voltages may -be orrepresent two tones, one of which represents mark` and the other spacein a frequency shift telegraphy system.

In describingv this inventionin detail, reference will be` made to the.attachedv drawings. wherein Fig.. 1 shows. by schematic diagram amechanical polar relay. This ngure is used to make. clear the need ofthis invention, and also to facilitate description of the invention.

Fig. 2. illustrates by schematic diagram the essential elements of theelectronic polar relay oi this invention.

Fig.2a is a chart showing the relation between voltages and theconducting conditions of the tubesv in arrangement of Fig. 2' in thepresence of certain control potential conditions which in turn mayrepresent certain signalling conditions, the successive rowsof thischart representing in general conditions at successive instants of time.

Fig.v 3 shows by schematic diagram the' essential. features of animproved two-tone telegraphy system using my improved high speedelectronic pol-'ar relay..

The benets that can be. obtained' in manyl applications', for example,in a two-tone telegraph system, through the use of a vpolar relay arewell known.

Heretofore, polar relays have been o1." the mechanical type. It is acharacteristicv of such mechanical" polar relays' that if the electriccurrent through the coils is reduced tozero, thel contacts. ofthelrelay" remain in their l-astoperated rov position. This is usuallyaccomplished through the use of magnetic pole pieces which havesufficient residual magnetism to hold the tongue of' the relay in itslast operated position in the absence of any electricl current throughthe coils.y In order to move the tongue of! the relay, it'is necessaryto reverse the current, through thecoil' or -cause current to flowthrough a diierent coil.

A two-tone telegraph system will be used.. to illustrate how a polarrelay can be employed. to advantage to assist in eliminating errorsintransmiss-ion. In such a system one tone frequency isl transmitted toindicate marking` intervals, and a dierent tone frequency is used forspacing intervals.

Fig. 1 is a` schematic diagram of a mechanical polar relay. Whenthisrelay is to be used with a two-tone telegraph system, the circuit isso arranged that Icurrent i1 is controlled by one of the tonefrequencies and i2 is controlled by the other tone frequency. Currentcan be made to flow either when the tone is present or when ittransmission circuit such that the spacing tone. no longer was received,thenV i2 would drop toy zero. Under this condition of no current flowingin either portion of.v the. coil', the relay would-remain in its lastoperated position by virtue of the. mechanical design of the relay andthe re' sidual magnetism in the pole pieces.

Suppose now that instead of the spacing toneI dropping out so thatneither tone was received.

an interfering, signal', is able.- to cause i1 to flow. Now 4both i1Vand i2 Iare flowing simultaneously. If, as is desirable, themagneti'zing. force produced by i1 is the same as that produced. by i2,

the resultant'magneti'zing,'force will become zero.;

Hence, the. netv result of both tones present is the same as neithertone present and` the operated position of the relay does not change.

Consequently, it is apparentv that if. the opere" ated position of therelay is. to be changed, the

spacing tone must go out and' the markingtone must come in. Thisv takesplace during normal two-tonetransmission. However, it' is veryim'-probable that spuriousl conditions and signals would cause one tone to'drop out' andv simulcuit of tube V4.

taneously cause another dierent tone of propel frequency to come in. Forthis reason, a polar relay used in conjunction with a two-tonesignalling system provides a very great protection against the recordingof false characters.

Among others, it is one purpose of this in- Vention to provide polaroperation at much greater speeds than those at which mechanical relaysare satisfactory. Fig. 2 is a schematic diagram of a circuit thatutilizes the control characteristics of vacuum tubes to simulate theoperation of a mechanical polar relay. Since a polar relay must be undercontrol of two separate and independent voltages or currents, two inputcircuits are provided, one for E1 andA one for E2. As shown in Fig. 2a,E1 is positive during marking signal and zero during spacing signal,while E2 is zero during marking signal and negative during spacingsignal.

Tubes or electron discharge systems V3 and V4 are connected in whatbasically is the familiar locking circuit. The circuit is so namedbecause of its property of locking intoA one or the other of its twostable positions, i. e., whenk the circuit is properly designed, eithertube V3 will be fully conducting and the plate current of tube V4 willbe Zero or tube V4 will be fully conducting and the current through tubeV3 will be zero.

is switched through V3 and cutoi occurs in V4. 1

When a potential such as to cause V4 to conduct is applied to the grid20, similar action switches the current through tube kV4 and cuts offtube V3.

In addition to the simple locking circuit, tubes V1 and V2 under controlof voltages E1 and E2 respectively are included. E1 is applied across aresistance R1 to the grid 49 of V1 which is biased by a source -C. Theanode 5I of tube V1 is coupled by resistance R2 into the anode circuitof Vsbetween'Rs and Re. The voltage E1varies from zero (see the chartFig. 2a), at which tube V1 is biased to cutoff by -Cto a positive valuei at which C is overcome and tube V1 conducts.

The voltage E2 is applied across R13 and to the grid 59 of tube V2, theanode of which is cou- This is because when tube V4 is biased at itsgrid 20 to cutoff, its` anode 24 becomes more positive (potential dropin R4 is less) as does the 4 be conducting with the result that themagnitude of the negative voltage supplied to the grid circuti of tubeV4 will be a maximum.

If the tubes, circuit components and supply voltages are properlyselected, the net negative voltage on the grid of tube V4 under normalmarking condition will be appreciably greater than is required tomaintain this tube non-conductive. In fact, it even Will be sufficientthat if E1 should fall to Zero (due to a fade out, for example) therebystopping the ow of current in tube V1 and increasing the positivevoltage cou- Apled into the grid 20 of tube V4, the net bias on pledinto the grid circuit of tube V4 @by anode load resistance R12. TheVoltage E2 varies from 0 at which tube V2, is conductive to a negativevalue at which tube V2 is cut o.

The plate circuit of tube V1 is interconnected with the plate circuit oftube V3 in such away that it 'can exercise considerable control over theamount .of positive voltage from the source Ebb that is available to becoupled into the grid cir- Tube V2 together with resistors R11 and R12constitute a voltage divider Ywith two possible settings. One setting isthat with tube V2 off. This is the condition of minimum negative biasvoltage (magnitude) supplied to V4. When tube V2 conducts, itshunts R12with the result that the magnitude of' the negative bias coupled intothe grid circuitfof tube V4 across R11 is increased. Consequently,thenet gridcathode voltage of tube V4 is ultimately under the control ofE1 and E2.

During the reception of a marking signal (E1 positive), tube V1 willconduct and reduce the amount of positive voltage coupled into the gridcircuit of tube V4. Simultaneously, tube V2 will the grid of V4 stillwould be suflicient to prevent space current in this tube. Or, ifinstead of E1 dropping out, E2 were to come in simultaneously with E1thereby reducing the magnitude of negative voltage supplied to the gridof tube V4 this tube still would not be able to conduct.

In order to change the sense of the output from the locking circuit, i.e., to cause current to flow in tube V4, it is necessary forboth tubesV1 and V2 to cease conducting. For this to take place E1 must drop tozero and E2 must become nega,- tive. These are two separate andindependent changes.

Under these conditions of tube V1 and tube V2 non-conductive, arelativelylarge positive voltage is coupled into the grid of tube V4from the source Ebb and a small negative voltage is supplied to the samegrid from Eea Now the net grid voltage of tube V4 will be Zero or evenslightlypositive. When, under these conditions, tube V4 passes current,the positive voltage coupled into tube V3 grid is reduced sufficiently,as a result of the potential 'drop in R4, to render tube V3non-conductive. When tube V2 ceases to conduct, the positive voltageapplied to the grid circuit of tube V4 is increased still farther.Consequently, tube V4 will continue to pass current,' even though eithertubes V1 or V2 should conduct individually for any reason.

To return tube V4 to the non-conducting condition, both tubes V1 vand V2must be made to conduct. This can take place only if voltage E1' becomespositive and E2 goes to zero.

The output may be taken at various points inv the tripping circuit. Forexample, the voltage or potential across R4 may be taken and used asdesired. Y

In the foregoing description the voltages E1 and E2 are referred toasrepresenting mark and space frequencies in a two-tone telegraphy system.Obviously, our improved high speed electronic polar relay may be put towide use in the radio and allied arts. All that is essential forcontrolling our polar relay is one voltage Which varies-.from zero to apositive potential, and a second voltage which varies from a zero to anegative value.

vWhen the voltages E1 and E2 represent twotone frequencies such as usedin a spaced Wave telegraphy system theymay be derived as i1lu`s`---\ 1 1are. Separated by the desired band of frequencies.

almanac,

The. separation should at least be sucient to per-mit separation of thesame in the circuits following the amplier and limiter stages. Aseparation of 400 cycles per second has been found satisfactory in oneapplication.

Circuit Vl2 is tuned so as to pass both tone frequencies. The amplifyingand limiting circuits of tubes 48, k53, $8 and 18 are substantiallysimilar and are well lknown in the art. Considering tube |8, forexample, lthe limiting action of the tube on positive input signals isimproved by resistor |9. Resistor 19 causes the grid of tube 18 to see arelatively high resistance generator as compared with the lowgrid-cathode resistance for `positive grid-cathode Voltage. As a result,voltages that cause the grid to become positive with reference to itsycathode are divided down by ra very high ratio. Further, thisgrid-cathode resistance is a non-linear function of current whichdecreases with increasing current so that when the input voltageincreases farther positive, the division ratio between the resistor I9and grid-cathode resistance of the tube increases. The net result isthat the positive peaks of input voltage are not present in the platecircuit of tube T8 because the grid cannot become appreciably positivewith -respect to its cathode.

The negative peaks of input voltage are not present in the platecircuitof the tube 18 either, due to plate ycurrent cutoii Thus we haveessentially symmetrical limiting as well Vas amplication in tubes 4,8,58,468, andl. Tubes 58 and 68 with resistances 59 and 69 operate liketube 'I8 as described hereinbefore.

The tone voltages representing mark are selected by tuned circuit Mendfed to an amplifier and coupling stage tube .80 while the voltagesrepresenting space are selected by a tuned circuit S and fed to anamplifier and coupling stage tube 90. The circuit M is resonated at themark frequency and the circuit S at the space frequency.

The oscillations of mark frequency are amplied by tube 80 and applied totube V1 across resistor 95. Tube V1 is a plate rectifier which gives adirect current output proportional to the peak lvalue of the sinusoidalinput signal. Resistors 96 and 98 are so proportioned that V1 -is at orbeyond plate current cutoi. lResistor 96 and capacitor 99 serve as an R.C. filter to isolate the power supply from signal circuit (with respectto A. C. variations) at rthe point shown. Resistor 94 prevents the grid49 from going more than slightly positive with respect to the cathodeand tends to flatten the plate current peaks of V1.

Assume that V3 is off and no signal voltage appears across resistor` 95.Capacitor |02 will have a `Voltage difference across its terminals equalto Ebb (approximately). `If signal is now applied to resistor `95, tubeV1 will conduct on the positive voltage peaks. Capacitor |02 willdischarge through tube V1 to some lower value of voltage, the dischargetaking place rapidly due to the small internal resistance of tube V1.'This voltage discharge occurs, of course, when V1 ,conducts due to apositive signal peak. When the input signal ,goes negative tube V1ceases conducting and capacitor |02 commences to charge back to Ebb.However, it must now charge throughRzi, R5 and Rs whose combinedresistance is much larger than the internal resistancel of V1. Thuscapacitor |02 will charge slowly (compared with a cycle of signalvoltage) and will not reach Ebb before V1 begins to conductagain. yConsequently, the voltage across capacitor |02 remains yatthe lowerpotential (except for a slight ripple) as long as signals of markfrequency are being received. When the signal ceases, the capacitorvoltage again rises to Ebb in a time that may lbe'equal to two or threetone cycles but which is small compared with the length of the shortestsignal element received.

Since the tube V1 is biased to cutoi by Een the potential at its anode5| is positive when the signal drops .out and less positive when signalcomes in. Thus lvoltage is coupled into the tripping circuits byresistance R21.

The space frequency voltages selected at S are amplified in tube andexcite the cathode |06 of a diode rectifier |08 the anode lof which iscoupled to the grid 59 of tube V2. The tube V2 is normally conductive.The `source Ebb produces across resistance ||0 a positive potential atthe cathode |06 end of said yresistance so that the diode |08 is biasedto cutoff normally. When space tone voltages come in the positive peaksthereof are ineffective. The negative peaks reduce the positivepotential on the cathode of the diode so that it passes current whichdevelops across resistance H2 a-negative potential to swing the grid 59negative -to -cut `off this tube and thereby reduce the negativepotential fed :by -Ecc to the grid y20 of tube V4. The condenser ||4smooths out the rectified pulses in about the same manner in which thepulses are smoothed out by condenser .I 02.

The operation ofthe two-tone systemv will now be described. In thisdescription which repeats the description of Fig. 2 given above,reference will be made to the chartof Fig. 2a.

With nosignal coming-into either channel, tube V1 is cut oiand tube V2conducts. If a marking signalcomes in, E1 becomes positive, turning tubeV1 on, making the grid Vof V4 .less positive. E2 is zero, andVzcontinues toconduct makingthe grid of V4 very negative. Thecombination of the two voltages ywill keep V4 shut off and allow V3 toconduct. If the marking signal drops Aout (indicated by dash in thesecond lineof Ithe first column of the chart) E1 .becomes zero, cuttingoff V1, making the grid of V4 more positive. E2 Aremains zero and V2remains on, keeping a high negative bias at V4. In this case thecombination of the Voltages keeps the grid of V4 below cutofLand V4 doesnot conduct. i

If the vspacing signal comes in E1 remains zero, V1 remains cutoff, andthe voltage at the grid-ofV4 remains the same due to this act. However,E2 becomes negative, shutting off V2 which raises the potential of thegrid of V4 to a point above cutoll". Inthis case vthe combination of thetwo voltages allows V4 to conduct, thereby shutting Voi V3. If thespacing signal drops out E1 remains zero and the IVoltage at the .gridof V4 due to V1 yremains the same. However, E2 goes to zero andi/2 againconducts, tending to ymake the voltage at V4 more negative. However, itis not sulcient to `drive the grid of V4 below zero, and V4 will remainon.

If a marking signal again comes in, E1 will again go positive, turningV1 on, lowering the potential of the grid of Vi to a point where thecombination -of `this voltage and the highly negative voltage due to V2remaining on turns Vi olf, thereby switching V3 on again.

Noise coming into the spacing channel while a marking signal is beingreceived may turn V2 olf, raising the grid potential of V4. However,this increase in grid Vvoltage is not suiiicient to make V4 .conductyand V3 Will remain on.

, comes in.

ing channel under these conditions, tube V1 will be turned on,decreasing the positive voltage coupled into the grid of tube V4. Inthis case, the decrease of positive grid voltage at V4 caused by theconduction of tube V1 is not sui'cent to drive said grid below zeropotential, and V4 remains on. The output is taken from the anode of tubeV4.

It should be realized that any good type of simple single coil(non-polar) relay may be used in `conjunction with the electronic polarrelay of Figs. 2 and 3, for example, connected in series with R4 asshown in Fig. 3, in order to obtain polar operation of a set of contactpoints.

To those versed in the art, many modifications of the basic inventionwill suggest themselves.

` As an example, separate circuits could be provided for adding voltagesE1 and E2 in a suitable manner and then applying their resultantvoltage, or one 'obtained therefrom, to a single point in a lockingcircuit.

What is claimed is:

1. Apparatus for keying including two electron discharge systems havinginput and output electrodes cross-coupled and biased to be alternativelyconductive and non-conductive, a iirst control tube biased to drawcurrent, a second control. tube Abiased to cutoiT, means for applyingalternatively present potentials to said rstV and second tubes toalternately bias said first tube to cutoff and said second tube to beconductive, and a connection between said rst tube and an inputelectrode of one of said systems, a connection between said second tubeand said input electrode of said one of said systems, thel connectionsand arrangement being such that one of said systems is made conductiveonly when both of said tubes are biased to be conductive and the otherof'said 'systems is made conductive only when bothl of said tubes arebiased to cutoi.

r 2.' An electronic polar relay including two tubes each having ananode, a control grid and a cathode, with the anodes and control gridscrossconnected, a direct current impedance interconand a fourth tubeeach havinga control grid and a cathode, means for applying independentsignals normally alternately present tothe control grid and cathoderespectively of said third and fourth tubes, a connection betweenthe'anode of the third tube and the control grid of said one tube, and aconnection between'the anode of the fourth tube and the control grid ofsaid one of said two tubes, the arrangement being such that when onesignal only is applied the said one tube has an output of a first value,which is maintained if said one signal drops outor said other signalcomes in, and whenthe other signal only is applied the said one tube hasan `output of avsecond value, and said output is maintained ifsaid-other signal drops out or said one signal 3. In a telegraphysystem, in combination, a

l rst pair of tubes each having a control grid, a

1 anodes cross-coupled so that a change of potential on Lthelanode ofone tube changes the ponectin'g the grid and cathode of one tube, athird8 tential on the grid of the other tube and vice versa, a second pair oftubes one of which is normally conductive and the other of which isnormally non-conductive, a coupling between the output of that one ofsaid second pair of tubes normally non-conductive and the anode of onetube of the rst pair of tubes, a coupling between the output of theother tube of said second pair and the control grid of the other tube ofsaid first pair of tubes, and means for applying potentials which appearalternately to the inputs of said tubes of said second pair of tubes.

4. In combination, two tubes having their control grids and anodescross-coupled by impedances so that when one tube is biased to cut oil'the voltage on the grid of the other tube becomes less negative and viceversa, a rst control tube having its output electrodes coupled with theanode of one of said tubes to vary the potential thereof and as aconsequence the potential of the grid of the other of said two tubes, .asecond control tube having its output electrodes connected by a voltagedivider to the control grid of the other of said two tubes to alsocontrol the bias on said grid, means for applying a bias potential tothe grid of said rst control tube which varies between a positive'valueand zero potential, and means for simultaneously applying to the grid ofsaid second control tube a potential which varies between zero potentialand a negative value.

5. In combination, two tubes having their control grids and anodescross-coupled by impedances so that when one tube is biased to cut o ithe voltage on the grid of the other tube becomes less negative and viceversa, a iirst control tube having a control electrode and outputelectrodes and having its output electrodes coupled with the anode ofone of said tubes to vary the potential thereof and .as a consequencethe potential of the grid of the other of said two tubes, means forbiasing said rst control tube to cutoff, a. second control tube having acontrol electrode and output electrodes and having its output electrodesconnected by a voltage divider to the control grid of the other of saidtwo tubes to also control the bias on` said grid, means for biasing thecontrol electrode of said second control tube by a potential such thatit is conductive, means for applying a control potential to the controlelectrode of said rst control tube which varies between a positive valueand Zero potential, and means for simultaneously applying to the grid ofsaid second control tube a control potential which varies between zeropotential and a negative value.

6. In a telegraphy system of the type wherein the signals arerepresented by two potentials of varying magnitude, alternativelypresent, two tubes each having electrodes including a, control electrodeand an anode and having their control electrodes and anodesinterconnected by impedances so that when one tube is biased to cutoli,-4

the voltage on the control electrode of the other tube becomes lessnegative, and vice versa, a rst control tube having a control electrodeand having output electrodes coupled directly to the control electrodeofone of said first two tubes to vary the potential thereon in accordancewith the signals, a second control tube having a control electrode and.having its output electrodes coupled directly tothe control electrodeof said one of said lirst two tubes to vary the potential thereon inaccordance with said signal potentials, means for applying one of saidsignal potentials to the control electrode of said first control tube,and

means for applying the other of said signal potentials to the controlelectrode of said second control tube.

EUGENE R. SHENK. JAMES R. WEINER.

REFERENCES CITED Name Date Herman 1 Mar. 10, 1931 Number Number 10 NameDate Finch Feb. 16, 1932 Schroter Nov. 28, 1933 Demarest Dec. 12, 1933Mathes Nov. 6, 1934 Callahan et a1. Aug. 5, 1935 Taylor June 30, 1935Powell July 26, 1938 Hansell Jan. 2, 1940 Humby et a1 Aug. 20, 1940Matusita July 22, 1941 Michel May 2, 1944

